Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

3. Extensions to Mendelian Inheritance

Penetrance and Expressivity

Genetics

3. Extensions to Mendelian Inheritance

Penetrance and Expressivity

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3:13 minutes

Problem 1

Textbook Question

Define and distinguish incomplete penetrance and variable expressivity.

Verified step by step guidance

Understand the concept of incomplete penetrance: Incomplete penetrance occurs when not all individuals with a particular genotype express the expected phenotype. For example, if a dominant allele is present but the phenotype is not observed in some individuals, this is incomplete penetrance.

Understand the concept of variable expressivity: Variable expressivity refers to the range of phenotypic expression among individuals with the same genotype. This means that while all individuals with the genotype express the phenotype, the severity or specific traits of the phenotype can vary.

Distinguish between the two concepts: Incomplete penetrance is about whether the phenotype is expressed at all (yes or no), while variable expressivity is about the degree or variation in the phenotype among those who do express it.

Consider examples to clarify: For incomplete penetrance, think of a genetic condition where some individuals with the mutation do not show symptoms. For variable expressivity, consider a condition like Marfan syndrome, where individuals may show a wide range of symptoms, from mild to severe.

Summarize the distinction: Incomplete penetrance is about the presence or absence of the phenotype, while variable expressivity is about the variability in the phenotype's manifestation among those who express it.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Incomplete Penetrance

Incomplete penetrance refers to a situation where not all individuals with a specific genotype express the expected phenotype. This means that some individuals may carry a gene associated with a trait or disorder but do not exhibit any observable symptoms or characteristics. This phenomenon can be influenced by various factors, including environmental conditions and interactions with other genes.

Variable Expressivity

Variable expressivity describes the range of phenotypic expressions that can occur among individuals with the same genotype. Even if individuals share the same genetic mutation, they may display different degrees of severity or types of symptoms. This variability can be influenced by genetic background, environmental factors, and lifestyle choices, leading to a spectrum of manifestations of a genetic condition.

Genotype-Phenotype Relationship

The genotype-phenotype relationship is a fundamental concept in genetics that describes how genetic information (genotype) translates into observable traits (phenotype). Understanding this relationship is crucial for distinguishing between incomplete penetrance and variable expressivity, as both concepts highlight the complexity of how genetic factors can influence physical characteristics and health outcomes in individuals.

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Related Practice

Multiple Choice

Which of the following statements is true of incomplete penetrance?

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Multiple Choice

If a geneticist describes a trait as being 70% penetrant, what does this mean?

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Multiple Choice

A group of individuals exhibit a range of intermediate phenotype between dominant and recessive. What term measures this phenotype?

Penetrance measures which of the following?

Brachydactyly type D is a human autosomal dominant condition in which the thumbs are abnormally short and broad. In most cases, both thumbs are affected, but occasionally just one thumb is involved. The accompanying pedigree shows a family in which brachydactyly type D is segregating. Filled circles and squares represent females and males who have involvement of both thumbs. Half-filled symbols represent family members with just one thumb affected.

Is there any evidence of variable expressivity in this family? Explain.

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Textbook Question

Is there evidence of incomplete penetrance in this family? Explain.

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Textbook Question

In goats, the development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the F₂ generation:

Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.

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Textbook Question

Discuss the topic of phenotypic expression and the many factors that impinge on it.

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